1. Field of the Invention
This invention relates generally to catheters adapted for use in surgical procedures and more specifically to catheters having inflatable balloons.
2. Discussion of the Prior Art
In many surgical procedures it is desirable to introduce an elongate flexible object into a body conduit and to enlarge the distal end of that object at an operative site. Catheters are well known to perform this function, and in one common variety a balloon is disposed at the distal end of the catheter to provide for the desired enlargement. When this balloon is inflated, it typically exceeds the radial diameter of the catheter.
Several surgical procedures, such as embolectomy and angioplasty procedures, take advantage of this balloon catheter construction. In an embolectomy procedure, the distal end of the catheter is introduced beyond a thrombus or embolus, the balloon is inflated, and the catheter with enlarged balloon is withdrawn. In this procedure, the enlarged balloon pushes the thrombus or embolus out of the vessel as the catheter is withdrawn.
In an angioplasty procedure, the balloon of the catheter is inflated in proximity to athroscorotic plaque. In this common procedure, the pressure of the balloon forces the plaque against the vessel walls hereby enlarging the flow path through the vessel. These and other techniques benefiting from balloon catheter technology are disclosed in the following patents which are incorporated herein by reference:
______________________________________ U.S. Pat. No. Inventor ______________________________________ 3,438,375 R. Ericson 3,866,599 C. Johnson 4,217,903 R. Witherow 4,254,774 J. Boretos 4,823,812 U. Eshel 4,913,701 A. Tower 5,036,868 A. Berggren ______________________________________
In all of these procedures, the initial diameter of the catheter is of particular interest. This elongate flexible structure is typically introduced through long, sometimes torturous, conduits in order to reach the operative site. In some cases, these conduits are quite narrow so that the diameter of the catheter is of critical importance. Such is the case with arteries in the hand of a patient. An embolectomy procedure performed in these environments might require a catheter having a diameter as small as 1 French.
The problem with achieving catheter diameters of this size has been significantly compounded in the case of balloon catheters. With these devices, the balloon structure has typically been provided on the outside of the catheter thereby increasing the diameter of the device. An inflation hole extends through the catheter wall into an inflation lumen of the catheter. The balloon with a cylindrical configuration is disposed over this hole and wound on the catheter body to form a seal on either side of the hole. By pressurizing the inflation lumen, an inflation fluid passes through the hole to inflate the balloon beyond the outer surface of the catheter body.
Attempts have been made to reduce the overall thickness of this balloon structure. The catheter wall has been thinned so that the diameter of the balloon windings can be formed in a recess. This has weakened the catheter walls so that the balloon windings tend to compress the lumen of the catheter. In some instances, metal bushings have been placed over the recess to prevent the collapse of the catheter walls. In such a combination, the total thickness of the catheter is determined by the thickness of four separate structural elements, the catheter wall, the bushing, the balloon and the winding. Since each of these elements has a cylindrical configuration, the wall thickness of each element is doubled in defining the diameter of the total construction. Thus, the catheter body provides two wall thicknesses in the overall diameter of the catheter. Similarly, the bushings, the balloon, the windings and any glue associated with the winding structure each add two thicknesses of material to the diameter of the catheter. As a consequence, eight layers of material have typically contributed to the overall thickness of the catheter.
In spite of the many disadvantages relating to the overall size of such catheters, the methods for constructing the catheter have demanded this configuration. The catheter body has typically been extruded, and any recesses provided in the catheter wall have been machined along with the inflation hole. Bushings have been placed over the recesses. The balloon in the initial form of a cylindrical elastic material has been positioned across the inflation hole and the balloon has been stretched and wound over the bushings. Gluing these windings in place has completed formation of the balloon structure.
Based on this method, typical of the prior art, the entire balloon structure has been formed on the exterior of the catheter body because of its accessibility. The detrimental effect on the overall diameter of the catheter has been accepted without recourse, but it has necessarily limited any possibility of providing balloon catheters in sizes smaller than 2 Fr.